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1500 questions
20
votes
3 answers
What's wrong with this code for tomographic reconstruction by the Fourier method?
I've been playing around with tomographic reconstruction algorithms recently. I already have nice working implementations of FBP, ART, a SIRT/SART-like iterative scheme and even using straight linear algebra (slow!). This question is not about any…
timday
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Frequency-domain zero padding - special treatment of X[N/2]
Suppose we wish to interpolate a periodic signal with an even number of samples (e.g. N=8) by zero-padding in the frequency domain.
Let the DFT X=[A,B,C,D,E,F,G,H]
Now let's pad it to 16 samples to give Y. Every textbook example and online tutorial…
finnw
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20
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Is there an algorithm to compute the phase for a single frequecy?
If you have a function $f(t)=A \cdot \sin(\omega t+\phi)$, and reference sin wave $\sin(\omega x)$ what would be a fast algorithm to compute $\phi$?
I was looking at Goertzel algorithm, but it doesn't seem to deal with phase?
SamFisher83
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3 answers
human speech noise filter
Does anyone know of a filter to attenuate non-speech? I am writing speech recognition software and would like to filter out everything but human speech. This would include background noise, noise produced by a crappy microphone, or even background…
rurouniwallace
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3 answers
Should the input of a Kalman filter always be a signal and its derivative?
I always see the Kalman filter used with such input data. For example, the inputs are commonly a position and the correspondent velocity:
$$
(x, \dfrac{dx}{dt})
$$
In my case, I only have 2D positions and angles at each sample time:
$$
P_i(x_i,…
Stéphane Péchard
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20
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3 answers
Meaning of Real and Imaginary part of Fourier Transform of a signal
Say $f$ is a signal of time $t$, $F$ its Fourier transform of the variable $v$.
It is known that in polar coordinate, $|F(v)|$ tells us how much the frequency $v$ is present over the signal, and $Arg(F(v))$ tells us how much the contribution of this…
user2682877
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20
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3 answers
FFT with asymmetric windowing?
Common non-rectangular window functions all seem to be symmetric. Is there ever a case when one would want to use a non-symmetric window function before an FFT? (Say if the data on one side of the FFT aperture were considered a bit more important…
hotpaw2
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4 answers
How do you calculate spectral flatness from an FFT?
Ok, the spectral flatness (also called Wiener entropy) is defined as the ratio of the geometric mean of a spectrum to its arithmetic mean.
Wikipedia and other references say the power spectrum. Isn't that the square of the Fourier transform? The…
endolith
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20
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3 answers
How does cascading biquad sections for higher order filters work?
I'm trying to implement an 8th order IIR filter and every application note and textbook I've read says that it is best to implement any filter of order more than 2 as second order sections. I used tf2sos in MATLAB to get the coefficients for second…
anasimtiaz
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20
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Cepstral Mean Normalization
Can anyone please explain about Cepstral Mean Normalization, how the equivalence property of convolution affect this? Is it must to do CMN in MFCC Based Speaker Recognition? Why the property of convolution is the fundamental need for MFCC?
I am very…
mun
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1 answer
Are there any analytic approaches to the design of quadratic polynomial filters?
The following paper describes an application of the Teager-Kaiser energy operator to x-ray image enhancement:
Reinhard Bernstein, Michael S. Moore and Sanjit K. Mitra, "Adjustable
Quadratic Filters for Image Enhancement" Proc. IEEE International
…
datageist
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20
votes
3 answers
What is the difference between linear and non-linear filters?
How a mean filter is called as linear filter and a median filter is called as non linear filter? I understand how a mean and median filter operates, but I was not able to relate with the term linear and non-linear. Please explain me with an example.
preethi
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3 answers
Why are magnitudes normalised during synthesis (IDFT), not analysis (DFT)?
In most examples and FFT code that I've seen, the output (frequency magnitudes) of the forward DFT operation is scaled by N -- i.e. instead of giving you the magnitude of each frequency bin, it gives you N times the magnitude.
Operationally, this is…
bryhoyt
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20
votes
3 answers
Difference between SNR and PSNR
I understood that SNR is the ratio of signal power to the noise power. In terms of images, how the original image is affected by the added noise. In PSNR, we take the square of the peak value in the image (in case of an 8 bit image, the peak value…
Premnath D
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6 answers
How to Generate Band Limited Gaussian White Noise in MATLAB?
In some papers, I read that the additive noise is band limited Gaussian white.
How can I simulate this type of noise use MATLAB?
Bo LI
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